User:Hugh Leyton/sandbox

Leyton 3-2 Transformer configuration

The “Leyton 3-2” Transformer configuration is an interconnection of Transformer Secondary windings to derive two-phase electrical power (2-φ, 180-degree phase rotation) from a three-phase (3-φ, 120-degree phase rotation) source.

The “Leyton 3-2” Transformer configuration evenly distributes all 120V & 240V loads, balanced across all three of the phases of the source. . The “Leyton 3-2” Transformer configuration, was devised for producing 120 / 240V from 480V or 240V, or even a 208V 3-phase sources in 2006 .

The concept is not new but does not appear to be known to many electricians. . It is now common practice with modern Generators which may be needed to produce different Voltages in the range of 110V to 500V, Single, Two or Three phase . . So modern Generators, confirm that this arrangement is common practice in some Power Engineering.

• Converting 3-phase to 2-phase 120 / 240V, as per the American House and Office Standard.
• Avoid the problems associated with 120 / 208V available from a normal 3-phase Supply.
• Balances all 120V and all 240V Loads equally across all three supply Phases.
• Particularly suitable for Load Balancing on Generators. Particularly suitable for 220V A/C

 <<  Diagram Fig. 1  >>
   Diagram of the "Leyton 3-2" Transformer configuration.

 = = = =  Still working on this article below here  
          Also  7 .png  Diagrams to go in somehow = = = =

Interconnection

This interconnection arrangement allows for regular three-phase supplies with currents equal on the three phases. Three phase is the common supply for Factories and large establishments. But the factory Offices still require regular 120 / 240V for their regular Lighting, computers and office equipment and 240V for their Air-conditioners. This Transformer Secondary interconnection configuration, thus provides the Office regular supplies from a 3-phase property supply.

 <<  Diagram Fig. 2  >>
   Modification to a standard "Star" 3-phase Transformer,
   for simplified "Leyton 3-2" Transformer configuration.

Definition

A “Leyton 3-2” Transformer configuration can be defined as any Transformer or multi Transformers, with three phases, where two of the 120° phase windings, connected in one way or another, to form a phase, at 180° to the first phase, thus providing a 120 / 240V Output from a 3-phase Input, which balances the 240V Load more or less equally across all three supply lines.

Technical Overview

This “Leyton 3-2” Transformer configuration, can be achieved by using three, standard, Off-the-shelf Single phase Transformers. The Primary side being connected to the 3-phase supply in the typical Delta configuration. It is the Secondary that has to be interconnected in this special arrangement. The three Transformers, ideally, should each have two 120V Secondary windings. A simpler or modified version can be done if there is only one 120V Secondary winding on each Transformer. Similarly, this arrangement can also be done, by minor modification to a three-phase Transformer that has its Secondary interconnected for 120V in a Star or Wye arrangement, but that does require one of the windings, originally connected to the Neutral point, be disconnected and reconnected to another Secondary winding. These two, still provide 120 / 240V and equally balance the 240V across all three supply phases, but does not balance the two 120V Loads, these have to be balanced manually, in the normal way.

 <<  Diagram Fig. 3  >>
  Simplified intrconnections of a 3-phase "Leyton 3-2" Transformer configuration.

The full, proper “Leyton 3-2” Transformer configuration, using two 120V windings on each of the three Transformers, provides both proper 120 / 240V and balances all 120V and all 240V Loads equally across all three supply phases. This is particularly advantageous for both good voltages for 220V Air-conditioners, and balancing loads across 3-phase Generators, thus avoiding uneven Engine wear, Alternator Hum and vibration, and premature bearing failure and assists steady voltage control. It also enables full Power availability from the supply Transformer KVA rating and or the Generators full Power.

How it works

It takes two of the 3-phases and combines them is such a way, that it halves the difference in their phase angles. Half way between 120° and 240° is 180°, that is exactly the phase angle we want, relative to the first phase at 0°. This is 60° from their normal phase. The second part of the mathematics is that, Cosine 60° = 0.5 Connect them so as to add the two 0.5 + 0.5 equals 1, which, in this case, produces 120V.

In a 3-phase Supply, the Transformer Secondaries, at one moment in time, we can select, when T1 is at 0° that is straight up in these drawings. At precisely the same moment in time, in this diagram, T2 is 120° from T1, shown here as 120° anti-clockwise. With T3 a further 120° from T2. If T1, T2 & T3 are all providing 120V, we can calculate all the vector voltages.

Note how T2 and T3 are both, exactly 60° from straight down, although on opposite sides of straight down. This means that T2 has a 0.866 vector at 90° which is 104V and a 0.50 vector at 180° which is 60V. T3 has a 0.866 vector at 270° and a 0.50 vector at 180° also 60V

 <<  Diagram Fig. 4  >>
  Diagrams showing Phase angles of a "Leyton 3-2" Transformer configuration.

So the T2 has a 0.866 vector at 90° is exactly opposite T3 has a 0.866 vector at 270°, they cancel out. But since both T2 & T3 have a 0.50 vectors at 180°, they can be connected in additive, thus giving 60V + 60V at 180° which is 120V in exact opposition to T1.

So this now provides two 120V phases relative to Neutral and 240V between each of the two phases. This is exactly the same as the Standard American supply to Homes and Offices. Wrongly called Single phase because as you can see, there are Two phases at 180° to each other. Which can also be called “Split phase” or as I prefer, to avoid confusion, 120 / 240V Supplies. ( Americans appear to only consider the 90° phase shift as Two phase, but the definition of Two phase does not specify the phase angle relationship. )

There is also a very small unequal problem, the copper resistance of T2 & T3 is twice that of T1 on its own. But copper losses in the windings should be relatively small in a Transformer anyway.

This demonstrates mathematically, how to get the two phases at 180° from each other and at the same voltage. Basically, this is a form of Phase Shifting Transformer Principles.

But it does not Balance all Loads on all Supply 3-phases, only the 240V Loads. Normal balancing practice would still be required to keep the 120V Loads balanced, but these might be small compared to the 240V Loads, particularly if used for Air-conditioning. But the full “Leyton 3-2” Transformer configuration does also balance the 120V Loads on all 3-phases.

Three Single phase Transformers

Transformer manufacturers do not appear to stock or readily supply these Three phase “Leyton 3-2” Transformer configurations at present. It is therefore probable that the Electrician may have to assemble three standard Transformers to provide this configuration. Three identical Transformers will be needed, each one must have two, 120V Secondary windings. The Primary winding to suit the 3-phase supply.

 <<  Diagram Fig. 5  >>
  The standard, full "Leyton 3-2" Transformer configuration,  
   showing Typical connections.     This could be a purpose built
 3-phase Transformer or three Single phase, standard Transformers.

It is preferable that these three Transformers be mounted side by side, maintaining ventilation space around them as per the manufacturers instructions. A single duct for the three High voltage wires, required from the high voltage Distribution Circuit Breakers, this will typically be 240V or 480V 3-phase, but could be any 3-phase voltage, as long as the Secondaries are 120V. A single duct for the three Low voltage wires, that is two Live wires and a Neutral. A Ground wire should also be included, because any Electrical source, Generator or in this case, Transformer, must have its Neutral, Grounded close to source, or at least conform to the necessary requirements. The Transformer metal cases must also be Grounded. There must also be ducts between the three Transformers for the Interconnecting wires.

It does not matter which Transformer is which, but it is advisable to identify them as T1, T2, T3. This “Leyton 3-2” Transformer configuration, usually identifies T1 as the principle or reference transformer. Its two 120V windings being connected in the typical 120 / 240V configuration, commonly used. It is the other two Transformers that have to be connected in the special arrangement, best explained by means of drawings. But it must be noted, that all Transformers might not be assembled and marked exactly the same, therefore the final two connections, must only be done after checking the voltages on the connections.

But if those T2 & T3 windings are connected the other way round, so they are in phase, that is at 0° with T1, then they can be connected in Parallel with the T1 winding, to double up on the Output Power. Since Standard “Off-the-Shelf” Transformers each have two 120V windings, we can repeat the same above connections, to provide the 180° phase, thus not only providing the two phases at 180° from each other and at the same voltage, but also ALL 120V and ALL 240V Currents will be shared equally across all Three supply Phases.

  <<   Diagram Fig. 6 >>
   The Interconnections of a "Leyton 3-2" Transformer   
   configuration constructed in 2007.
  

File:Fig. 6 Interconnections of a 'Leyton 3-2' Transformer configuration.png

Fig. 6 The Interconnections of a "Leyton 3-2" Transformer configuration constructed in 2007.

It had been assumed that this was a very common connection practice, but so far similar arrangements have not been found, Transformer manufacturer who makes these 3-phase Transformers, do not list these, nor has this been seen, elsewhere. So it is now being calling the “Leyton 3-2” Transformer configuration, not to be confused with the “Scott-T” connection which only gives 90° shift. It should be noted here, that large Generators have been using a similar arrangement for many years, for the same purpose. Modern, Standard Generators can provide many different configurations.

Alternative Methods

Presently, it is quite common to supply 120 / 240V from a 3-phase Delta supply, by centre tapping one of the three 240V phase windings. However, this limits each 120V Load to only 5% of the transformer KVA rating and the whole transformer must then be de-rated by 30%. It also leaves one phase High at 208V which can’t be used for any regular purpose, so also unbalances the 3-phase supply. Another alternative is to use a separate Utility Supply for the 120 / 240V from the Utility 3-phase supply. This of course, has problems if a Stand-by Generator is to be used, or if two Meters are not wanted.

Apparently a common alternative is to just connect the 208V supply to all equipment requiring 220V - 240V, this is a very bad alternative, because the 208V at the supply point, will typically be only 195 – 185V at the Air-conditioner terminals and will seriously shorten the life of the compressor motors, it also voids the guarantee on such equipment. Sometimes, the 220V Loads can be supplied from a 208V source, via Boost Transformers. This is good for the equipment, but complicates the Distribution panels, and does not balance the loads across all three phases. Perhaps acceptable, if the 220V Loads are small compared to the whole site loads.

Unbalanced loads

With this “Leyton 3-2” Transformer configuration, there are no unbalanced loads on the 3-phase supply. All 120V Loads and all 240V Loads are evenly balanced across all three Input supply phase wires, with the Full “Leyton 3-2” configuration. Each of the two 120V Loads can be close to 50% of the total configuration capacity, the 240V Loads could be up to 100% of the configuration capacity. Unlike centre-taping 240V Delta Transformers for two 120V where each one is limited to only 5% of the transformer KVA rating and the whole transformer must then be de-rated by 30%. This configuration has no such balancing issues. Also, with this “Leyton 3-2” Transformer configuration, there is no “High” phase left that can’t be used for Single phase use. The output of this configuration can go into regular Office type Distribution Panel Boards, with no restrictions, making wiring and expansion very simple and normal.

Normal allowances have to be made, just as with any other Transformer, for Power Factor Loads and non-linear loads causing Harmonics.

Typical Site

In a Typical Site that requires 3-phase, the utility supply may well be 480V 3-phase. This would go to a 480V 3-phase Distribution, it might even come via a Change-over Switch with a Generator on the other side. This 480V 3-phase would be distributed out to all the 480V Machinery and Motors as required. Also to a “Leyton 3-2” Transformer configuration, for all the regular 120 / 240V Distribution around the site and the Office etc.

  Test diagram only  - Wrong drawing to prove that the code works.

Fig. 6 The Interconnections of a "Leyton 3-2" Transformer configuration constructed in 2007.

   <<  Diagram No. 7   >>
     Typical Site, with a 3-phase Supply & Generator, 
      supplying 480V 3-phase & regular  120 / 240V

Currents & Cable Sizes

Both the input cables and output cables must be sized according to normal practice, except the Input is 3-phase, the output is 120 / 240V. For example, a 100 KVA “Leyton 3-2” Transformer configuration, will draw about 125 Amps per phase from a 480V supply, so that would be about 250 Amps per phase from a 240V supply, depending on Transformer efficiencies. However, the 120 / 240V Output could deliver up to about 415 Amps on each of the two phases, L1 & L2, so the Neutral should be sized for about 200 Amps, to cater for serious imbalance use of the two 120V lines. Not forgetting that for a 100 KVA configuration, three 50 KVA Single phase Transformers are required.

See also

1. Scott-T transformer
2. Alternating current
3. Polyphase coil
4. Symmetrical components
5. Alternator
6. Three-phase electric power
7. Zigzag transformer
8. Split-phase electric power
9. Mains electricity

120/240V electric power from 3-phase

The 120 / 240 Volts Electric power is the normal standard for most residential and Office buildings of North America. Usually this is supplied by a Single-phase electric power supplied from a single Transformer. However, to obtain both the 120 Volts and the 240 Volts, a Split-phase electric power is normally used. A split-phase electricity distribution system is a 3-wire distribution system, commonly used in North America for single-family residential and light commercial (up to about 100 kVA) applications. Since there are two live conductors in the system, some electricians will say, "it is sometimes incorrectly referred to as "two-phase" ". This is wrong, there is nothing in the definition of Two-phase, to define the phase angle between them. In the common 120 / 240V system, the two live or "hot" conductors' waveforms are offset by a half-cycle, or 180 degrees offset, when measured against the neutral wire. So this is also a Two-phase system, but to avoid confusion with split-phase 90 degrees offset, Scott-T transformer motor start applications, it is usual to call this power distribution system a 3-wire, single-phase, mid-point neutral system.

Fig. 1 Split-phase Transformer, 120 / 240V.

This 120 / 240 Volts is the most common electrical power supply in the USA and other countries following the USA standard, but the 460V is not common in Europe, where the normal supply is 230V Single phase, that is One “hot” wire and Neutral.

Some of the confusion is that a motor with just two wires can correctly be called a Single-phase motor, regardless of, its voltage, 115V or 230V. But any Supply with two "hot" conductors' and a Neutral, is Two-phase, just as three hot wires is a 3-phase supply.

3-phase for Larger Loads

However, for larger loads and where 3-phase motors and other 3-phase equipment is used, then Three-phase electric power is a common method of alternating-current electric power generation, and distribution.

Left: Six-wire three-phase alternator, with each phase using a separate pair of transmission wires. Right: Elementary three-wire three-phase alternator, showing how the phases can share only three wires.

At the customer, this 3-phase is normally supplied from a Star or “Wye” Transformer, which has the 3-phase wires and a central Neutral. Typically 120 / 208 Volts, for 120V Single-phase power for Lighting and general use. That gives three individual 120V supplies, but has only 208V between the phases.

Alternatively the customer supply, can be supplied from a 240V 3-phase Delta Transformer, with a Grounded Neutral connection in the centre of one of the 240V windings, to provide two 120V supplies. [1]

One voltage cycle of a three-phase system

From Polyphase system :

Single-phase loads from 3-phase source

Single-phase loads may be connected to a three-phase system in several ways. Either a load may be connected across two of the live conductors, or a load can be connected from a live phase conductor to the neutral conductor. Single-phase loads should be distributed evenly between the phases of the three-phase system for efficient use of the supply transformer and supply conductors. If the line-to-neutral voltage is a standard load voltage, for example 120 volt on a 208 volt three-phase system, single-phase loads can connect to a phase and the neutral.

Lighting and receptacle outlets are connected from either phase conductor to neutral, giving the usual 120 V required by typical North American appliances. This practice is common enough that 208 V single-phase equipment is sometimes available in North America, but not available in many places. Attempts to use the more common 120/240 V equipment intended for split-phase distribution may result in poor performance since 240 V heating and lighting equipment will only produce 75% of its rating when operated at 208 V. Motors rated at 240 V will draw higher current at 208 V.

Problem with Low voltage to Air-conditioners

But worse still, is connecting compressor motors, such as Air-conditioners, designed for 240V supplies, to 208V supplies. That can cause damage to the motor or even burnout, should the motor fail to start turning, known as “locked rotor”.

There are various other ways to get 120 / 240V from a 3-phase supply. A Split-phase electric power distribution system is a 3-wire single-phase distribution system, commonly used in North America for single-family residential, offices and light commercial to get 120 Volts and 240V.

In North America, the high-leg delta system allows single-phase 120 V loads and 240 V three-phase loads both to be served by the same three-phase. A variation is the 240 V delta 4-wire system, also known as a high-leg or red-leg delta.

High-leg delta

High-leg delta is a type of electrical service connection, it is sometimes used where both lighting and three-phase motor loads were fed from the same distribution system.

Center-tapped delta transformer, bottom secondary winding giving 120-0-120V & 240V Primary windings shown in the centre.

This is a three-phase 240 V delta connected system, in which one winding of the transformer has a centre tap which is connected to ground and used as the system neutral. This allows a single service to supply 120 V for lighting, 240 V single-phase for heating appliances. But has Disadvantages, since one phase-to-neutral voltage (phase 'B') is higher than the others, 208 V to neutral, no single phase loads can be connected to this phase. This eliminates the ability to use one third of the breakers in a panel for single-phase loads. Further, the lack of loading on the high leg will result in an unbalanced load. Which leads to a number of problems, electricians can easily make a mistake and connect 120V equipment to this 208V “high leg”. It makes distribution boards more complicated. It results in unbalancing loads on the 3-phase supply. Such Transformers are normally limited to only 5% of the Transformer rating on each of the two 120V legs and the whole Transformer must be derated by 30% [2]

All these various ways can result in unbalanced loads on the 3-phase supply. This will reduce available power from a supply Transformer, but much worse, it can cause problems on supply Generators and Stand-by Generators.

120/240V electric power from 3-phase Transformer

There is, however a better way. A 3-phase Transformer can have its 120V Secondary windings connected in a way, similar to Generators, to provide true, proper 120 / 240V supply and if there are two 120V Secondaries on each of the three phases, identical to modern Generators, [3] [4] then a full Load balance can be achieved for all 120 Volt and 240V loads across all three supply phases. Power transfer into a linear balanced load is constant, which helps to reduce generator and engine vibrations, premature bearing damage and help maintain steady Voltage control.

Vector sum of the magnetic field vectors of the stator coils produces a single rotating vector of resulting rotating magnetic field.

This picture shows the relationship between the three phases. It is the same regardless whether the magnetic field is rotating physically, as in a generator, or rotating electrically as in a 3-phase Transformer, but easier to visualise if physically rotating. If the Neutral point is taken between one phase and the other two phases, the resultant end voltages will be 120 / 240V.

With only one 120V Secondary winding per phase, all three windings are connected in Series with each other and Neutral connected between one winding and the other two windings. However, if there are two 120V windings per phase in a suitable 3-phase Transformer, then the six 120V windings are connected similar to diagram (FF) [3] Which gives 120V from either end to the Neutral mid-point and 240V across end-to-end. This can also be achieved using three standard, “off-the-shelf”, single-phase Transformers. All 120V and all 240V Loads will then be shared equally across all three supply phases.

See also

1. Electrical wiring in North America
2. Electric power system
3. Mains electricity
4. Power engineering
5. Alternating current
6. Three-phase electric power
7. Two-phase electric power
8. Single-phase electric power
9. Split-phase electric power
10. High-leg delta
11. Polyphase system
12. Scott-T transformer
13. Zigzag transformer
14. Diesel generator
15. Alternator
16. Symmetrical components

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